how to save ppp-out uptime?

Hello,
I want to save the ppp-out uptime (how much time the modem is connected )
but I couldn’t find how
I don’t have Uptime in the command -

:put [/interface ppp-client get ppp-out1 
add-default-route       dial-on-demand     mrru        profile       
allow                   disabled           name        remote-address
apn                     info-channel       null-modem  running       
comment                 keepalive-timeout  password    use-peer-dns  
data-channel            max-mru            phone       user          
default-route-distance  max-mtu            pin         value-name    
dial-command            modem-init         port

so where is it?

Thanks,